Semiconductor wafers and other substrates may be provided with indicia, such as optical character recognition (OCR) scribes and/or barcodes, that identify, among other things, the wafer number and manufacturer. The indicia may be, for example, 5/8 to 3/4 inches in length and are typically provided on the wafer as a matrix of laser-etched pits.
The markings are generally provided as a relatively low-profile, rectangular field, which may be on the top or bottom surface of the semiconductor wafer. The wafers are generally processed with their top surface facing upward; however, in some applications, such as profile measurement of raw wafers, wafers are processed in both top up and top down orientations. Moreover, while wafers typically bear indicia on the top wafer surface, some wafers are marked on the bottom surface.
Heretofore known optical character recognition systems have been designed to read only one scribe window, i.e., they read only indicia that are in the normal field of view of the camera. To read indicia on both sides of the substrate using conventional systems requires the use of two cameras and illumination systems. This requires a second system that would intrude significantly into the space below the wafer otherwise used by a process machine. The utilization of a second system disadvantageously requires substantial modification of the process machine to accommodate the second system.